The instant invention is related to Reeves type variable speed transmission devices and more particularly to a programmable speed selector therefor.
A Reeves type variable speed transmission unit comprises a pair of split pulleys with a drive belt extending around both pulleys. Speed adjustment of the pulley arrangement is accomplished by means of a worm screw arrangement which is operative for adjusting the distance between the two halves of one of the split pulleys. The worm screw includes a crank shaft which is manually rotatable for adjustment of the spacing of the pulley halves, and the Reeves drive includes a speed indicator for indicating the speed at which the Reeves drive is set. Adjustment of the speed of the Reeves drive is accomplished through manual rotation of the crank shaft and visual inspection the speed indicator to determine when the desired speed is reached. Rotation of the hand crank in a clockwise direction decreases the speed of the drive; and rotation in a counterclockwise direction increases the speed of the drive.
Reeves type transmission units have heretofore been known in the art for providing variable speeds in milling machines and other mechanical machinery. The milling of machine parts often requires the use of several different milling tools each of which requires a different rotational speed of the milling machine, and the Reeves drive enables the milling machine to be readily adjusted to the required speeds. However, it has been found that repeated manual adjustment of the speed of a milling machine is inefficient and inconsistent, thereby causing inconsistent milling results.
Heretofore, motorized speed changing devices for Reeves drives have been known in the art. In particular, Warnke Tool Industries of Oxford, Mich., manufactures such a device which comprises an electric motor that attaches to the crank shaft portion of the worm screw, and a rheostat switch which is operative for controlling rotation of the worm screw in clockwise and counterclockwise directions. Although this device facilitates rotation of the worm screw, it does not provide any means for automatically selecting a desired speed.
The U.S. Pat. No. 3,216,268 to Moser et al also discloses a motorized apparatus for adjusting the speed output of a Reeves type transmission unit. More specifically, the Moser patent discloses a vernier adjustment mechanism for making very fine adjustments of the Reeves drive. The apparatus includes an electric motor which is coupled to the worm screw of the drive through a gear mechanism, and a control unit which is operative for controlling operation of the motor.
Still further, computer numerical control (CNC) systems have been known for programming milling operations and automatically controlling a milling machine according to a set program.